Networks that primarily utilize data link layer devices are often referred to as layer two (L2) networks. A data link layer device is a device that operates within the second layer of the Open Systems Interconnection (OSI) reference model, i.e., the data link layer. One example of a common L2 network is an Ethernet network in which end point devices (e.g., servers, printers, computers, etc.) are connected by one or more data link layer devices referred to as Ethernet switches. The Ethernet switches forward Ethernet frames, also referred to as L2 frames, L2 communications, L2 packet data units (PDUs), or L2 packets, to devices within the network. As the Ethernet switches forward the Ethernet frames, the Ethernet switches learn L2 state information for the L2 network, including media access control (MAC) addresses for the devices within the network and the physical interfaces of the Ethernet switches through which the devices identified by the MAC addresses are reachable. The Ethernet switches store the association between physical interfaces and MAC addresses in learning tables associated with each of their physical interfaces. When forwarding an individual Ethernet frame, an ingress interface of an Ethernet switch typically broadcasts the Ethernet frame to all of the other physical interfaces of the switch unless the Ethernet switch has previously learned the specific physical interface from which the destination MAC address specified in the Ethernet frame is reachable. In this case, the Ethernet switch forwards a single copy of the Ethernet frame out the associated physical interface. While referred to as interfaces in this disclosure, these interfaces are also commonly referred to as “ports.”
Recently, network service providers have offered systems that provide L2 connectivity between multiple, geographically separate L2 customer networks. That is, the L2 customer networks may be interconnected by the service provider to provide L2 connectivity as if the L2 customer networks were directly connected. One mechanism by which network service providers provide L2 connectivity to their customers is Virtual Local Area Networks (VLANs). VLANs are a generic grouping mechanism for Ethernet frames that allow logical isolation of multiple L2 networks that share the same physical Ethernet interfaces. In other words, a service provider may associate different VLANs with different customers so that L2 traffic and L2 state information for the networks, e.g., learned MAC addresses, are logically separate for the customers. VLANs allow network switches and other infrastructure of the service provider to multiplex the L2 customer traffic over shared physical Ethernet interfaces. In this way, each VLAN provides a connection between devices assigned to the VLAN, and each of the VLANs may be considered an independent layer two (L2) network. A device assigned to one VLAN can communicate with other devices on that VLAN but may be unable to communicate with devices on a separate VLAN. Ethernet frames for different VLANs may be correctly forwarded within a network by appending a VLAN tag to the frames to designate the VLAN to which each frame belongs. Network switches within the service provider network forward the Ethernet frames using the MAC addresses and other state information learned for the specific VLAN.
In some networks, such as Metro Ethernet Networks (MEN), the network service provider contracts with a network operator to utilize existing infrastructure, such as copper telephone lines, to deliver data or Internet services to the customers of the network operator. Often, the service provider in this arrangement is referred to as an Internet service provider (ISP). Using the existing network infrastructure owned and operated by the network operator, the ISP provides data or Internet services to which one or more customers of the network operator may subscribe. In this arrangement, the network operator may contract with a number of different ISPs to provide customers of the network operator with a choice of services at competitive prices. This network operator is considered a wholesaler of layer two (L2) connectivity in that the network operator offers L2 connectivity for use by any ISP, where layers in this disclosure refer to layers of the Open Systems Interconnection (OSI) model.
While this arrangement between network operator and ISPs benefits the customers of the network operator in terms of competitive pricing (which increases the network operator's desirability from the customer perspective), such an arrangement often results in complications. For example, complications often arise when ISPs attempt to provide new L2 connectivity services in that these services do not scale well to accommodate the typically large number of customers of a network operator. For example, so called “E-LINE” service, also known as Virtual Leased Line (VLL) or Ethernet Private Wire Service (EPVS), provides point-to-point (P2P) connectivity. “E-LAN” service, also known as Virtual Private LAN Services (VPLS) and Transparent LAN Services, provides multipoint-to-multipoint (MP2MP) connectivity in which there is no communication restriction between devices. A third type of metro Ethernet service, referred to as “E-TREE” service, has recently been defined in which Ethernet communication is constrained to point-to-multipoint (P2MP). Often, the lack of scalability occurs because of limitations of network devices owned and operated by the network operator rather than the ISPs. The inability of the network operator to successfully enable these ISPs to provide these new services may reduce the number of ISPs willing to provide services for that network operator and drive customers to a competing network operator that can provide these services.